The compressor of a turbine engine is located in advance of the combustor and the multi-stage turbine assembly. The compressor functions to incrementally compress air and to move the air longitudinally through the compressor and into the combustor. A metered amount of fuel also is directed into the combustor, and is burned with the compressed air. The resultant energy transfer creates high velocity gas flow which is directed to the multi-stage turbine assembly. The turbine assembly, in turn, drives the compressor of the turbine engine and also produces the required power or thrust for the aircraft or other vehicle in which the engine is installed.
The compressor typically includes alternating arrays of rotating and stationary vanes which are arranged in stages along the longitudinal axis of rotation of the compressor. The rotating member in each stage functions to both compress the air and to advance the air longitudinally to the next successive stage. The stationary arrays of vanes, or radial impellers, function to guide the air into the next rotating array at the proper angle.
The compressor typically includes a plurality of bleed valves which are programmed to release air from the compressor at the onset of operating conditions that might otherwise result in a compressor instability referred to as surge or stall. For example, it is important for the bleed valve to be closed when the engine is operating at rated power or thrust. However, during other operating conditions such as certain ranges of acceleration, deceleration and other low pressure operations, the compressor bleed valves are opened to release air from the compressor, thereby avoiding compressor instabilities.
The specific conditions under which the bleed valve is opened, closed, or modulating therebetween typically are controlled by the transient air bleed actuator which senses certain engine operating characteristics, such as core compressor speed and fuel flow parameters. The specific conditions at which the bleed valve should open and close vary from engine to engine. Typically it is necessary to conduct bench tests on each engine to determine and calibrate the precise setting of the transient air bleed actuator. Precise setting of the transient air bleed actuator is critical in that a closed setting that is too low results in the probability of engine surge. On the other hand an open setting that is too high may prevent the engine from making power under certain operating conditions.
After the turbine engine is accurately set by bench testing with sophisticated equipment, the engine then is installed in the aircraft or other vehicle. Frequently this installation is carried out at a location far removed from the place of manufacture of the engine. The structure in which the engine is mounted frequently will have a significant installation effect on the aerodynamic performance of the engine. As a result, it invariably is necessary to reset either the transient air bleed actuator or the various engine parameter affecting the operation of the compressor bleed valve. For example, the fuel control schedule may be adjusted in the field to match the actual operation of the compressor bleed valves on the installed engine. This resetting or recalibration can have a very important effect on the ability of the engine to perform properly in actual use.
The ability to precisely reset the engine after it has been installed is dependent upon the ability to accurately determine the point at which the compressor bleed valves just begin to open. In the past, procedures for establishing the open and closed positions of the air bleed actuator have been imprecise. For example, ground crew personnel have tried to rely upon engine sound to determine the desired steady state bleed open and closed points. Specifically, the operator would slowly decrease the throttle levers in the cockpit and mechanics would try to listen for the initial escape of air from the air bleed valves. Other personnel have relied upon the cockpit instrumentation. Thus, for example, on a turbofan engine, during a slow, steady state deceleration the operator of the engine would closely observe the relationship between core speed and fan speed. As the core speed decreases, the bleed starts to open and the fan speed begins to decrease at a faster rate. Still others would listen for engine vibrations to determine the just beginning to open point.
These known methods for setting or calibrating the transient air bleed actuator have been extremely undesireable. For example, the audible signals from the engine could be interpreted differently by each individual operator. Furthermore, since all engines are different in some respects, similar audible signals given by two engines could actually reflect quite different operating conditions. Similarly, tests which rely upon cockpit instrumentation have been unreliable since the cockpit instruments are not calibrated to detect the specific operating points which correspond to bleed open or bleed closed conditions.
Consideration had been given to constructing instrument dials that could precisely measure selected engine operating parameters, and that could accurately identify the conditions corresponding to bleed open or bleed closed. However, the instruments and dials required to identify the specific operating points would be extremely large and expensive. Furthermore, most of the information relayed by these large expensive instruments would be largely irrelevant since it would be only a single point on the dial that would be of interest.
Simple pneumatic devices which measure pressure levels have been developed. Such devices are shown in: U.S. Pat. No. 2,706,463 which issued to Dunn; U.S. Pat. No. 3,024,655 which issued to Dwyer et al; U.S. Pat. No. 3,208,425 which issued to Jousma et al; and U.S. Pat. No. 4,169,386 which issued to McMahan. Although these devices can be manufactured inexpensively, they generally suffer from the same drawbacks as the pressure measuring dials. Specifically the known devices provide an approximate indication of pressure level, but are not able to accurately indicate a small pressure change or reversal. Furthermore they have not been considered for use with turbine engines.
Accordingly it is an object of the subject invention to provide an apparatus for calibrating or setting the compressor air bleed valve schedule.
It is another object of the subject invention to provide an apparatus for precisely identifying the engine operating conditions at which the air bleed valves just begin to open.
It is a further object of the subject invention to provide an apparatus that can be used in calibrating the fuel control schedule to reflect actual operation of the compressor bleed valves.
It is still another object of the subject invention to provide an apparatus for identifying changes or reversals in pressure, and flow, including small pressure changes in system accomodating high pressure levels.
It is still a further object of the subject invention to provide an apparatus that can be constructed inexpensively, that is sturdy and that can be used under a variety of conditions.